I believe the key to this would be the seal of the cab and insulation. If you have wind coming through holes and little insulation in those temps I don't think the heater can compete. However, these cabs can be sealed up tight and relatively easily insulated. At that point you have a fan running through 180 degree heater core and the air does come out hot in these trucks. As you may know, there are few types of heaters for these trucks. While the deluxe fresh air is more sought after, the recirculating heater might be better for cold climes by not taking in the cold fresh air. Good luck.
